It is known that a cardiac tachyarrhythmia can be converted to a rhythm that is more physiologically tolerable through the proper application of electrical energy. This process is commonly referred to as cardioversion.
Cardioversion requires the detection of the arrhythmia, or its onset, prior to the application of electrical energy. Within the setting of a modern hospital, this function may be performed with some efficiency. To effect cardioversion in other settings, there have been efforts directed toward the development of an implantable unit to detect and respond appropriately to an arrhythmia. Within an implantable unit, a major difficulty is the determination that cardioversion is necessary.
U.S. Pat. No. 3,805,795 issued Apr. 23, 1974 and entitled Automatic Cardioverting Circuit discloses fully implantable circuitry for detecting the development of a life threatening arrhythmic condition to automatically apply an electrical shock to the heart to restore normal heart activity. The detecting or sensing system of the referenced patent monitors two dynamic characteristics of the heart and defines the absence of both of those characteristics, for a predetermined period of time, as an arrhythmic heart condition. Thus, the device of the referenced patent detects an arrhythmic heart condition only after that condition has developed.
U.S. Pat. No. 3,937,226, issued Feb. 10, 1976 in the name of Herman D. Funke and entitled Arrhythmia Prevention Apparatus, which application is co-owned with the present invention, discusses the disadvantages of cardioversion after development of the arrhythmia. As stated in the Funke application, these disadvantages include higher power requirements and time delays. To overcome these disadvantages, Funke has proposed a system the use of which is intended to prevent the development of fibrillation or other arrhythmias. Essentially, the system senses heart depolarization at a plurality of areas on the heart through a plurality of electrodes connected in spaced relation to the heart. A depolarization occurring at any area on the heart is first sensed by any one of the electrodes and then transmitted to a stimulation device which supplys stimulation pulses to the entire plurality of electrodes connected to the heart. The stimulation thus provided is intended to counter the development of the arrhythmia. However, this system has significant power requirements as a result of its regular application of stimulation energy to the heart.